1. Field of the Invention
The present invention relates to a power adjustment apparatus which connects a phase shifter to a power-system bus and controls the phase shifter to continuously adjust the active power or reactive power.
2. Description of the Related Art
Conventionally, the power of a large-capacity load is adjusted by, except when the load itself has an adjusting function, connecting the load to the secondary side of a tapped transformer and changing the magnitude of a voltage to be supplied to the load by changing the tap, thereby adjusting the active power or reactive power consumed by the load.
Unfortunately, the operation of the tapped transformer is to change the voltage stepwise by a tap changer. Therefore, the tapped transformer is unsuitable to finely adjusting a voltage in accordance with the state of a system. Also, tap changing takes a long time, and the operation cost increases because the tap changer requires frequent maintenance.
It is also possible to perform adjustment rapidly and continuously by using a power electronics type power converter. However, the method requires a high cost and relatively increases power loss.
Meanwhile, proposals for realizing continuous voltage control by using an induction type phase shifter (to be referred to as a xe2x80x9cphase shifterxe2x80x9d hereinafter) have been made. Proposed methods of this type are a first method in which the phase shifter is connected in series with a bus (e.g., Jpn. Pat. Appln. KOKAI Publication No. 10-322910 (original application is U.S. patent Ser. No. 08/814,374), Jpn. Pat. Appln. KOKAI Publication No. 2001-157365 (original application is U.S. patent Ser. No. 09/443,220), and Jpn. Pat. Appln. KOKAI Publication No. 2001-169462), and a second method in which the phase shifter is connected in parallel with a bus (Jpn. Pat. Appln. KOKAI Publication No. 62-50913).
In the first method, to suppress power fluctuations, power is passed through the phase shifter to adjust the active power or reactive power. Therefore, the phase shifter must be given a capacity which allows the total power to pass through. This requires a large-capacity phase shifter. In addition, maintenance and the like are very difficult to perform because the phase shifter is connected in series with a bus.
In the second method, the phase shifter is connected in parallel with a bus, so fluctuations can be controlled without any passage of power. Therefore, the phase shifter need only have a capacitor corresponding to the fluctuations. In addition, maintenance and the like can be performed only by disconnecting the phase shifter from the bus. This makes the maintenance and the like very easy to perform. However, the purpose of the second method is to adjust only the reactive power, so a transformer is connected in parallel with the phase shifter. Also, the second method particularly adjusts the lagging reactive power. Hence, the leading reactive power and the active power cannot be adjusted.
It is an object of the present invention to provide a power adjustment apparatus which can perform fine adjustment in accordance with a load power command and which reduces power loss.
A power adjustment apparatus according to a first aspect of the present invention is characterized by comprising: a phase shifter including a stator having a stator winding and a rotor having a rotor winding, a winding terminal of one of the stator winding and the rotor winding being connected to a power-system bus, and a winding terminal of the other being connected to the power-system bus via an impedance load; a driver axially coupled to the rotor to drive the rotor; and a controller which outputs a command to the driver value to adjust a phase difference between the stator and the rotor to a desired value.
A power adjustment apparatus according to a second aspect of the present invention is characterized by comprising: a phase shifter including a stator having a stator winding and a rotor having a rotor winding, winding terminals of the stator winding and the rotor winding being connected to a power-system bus; a driver axially coupled to the rotor to drive the rotor; and a controller which outputs a command to the driver value to adjust a phase difference between the stator and the rotor to a desired value.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.